The present disclosure relates to image forming apparatuses and sheet conveyance apparatuses, and in particular, to those capable of electrostatically attracting and conveying a sheet using a conveyance belt.
An inkjet printing system is well known as employed in an image forming apparatus, such as a printer, a facsimile, a copier, a multiple function machine, to form an image by printing, duplicating, and imaging while adhering liquid drop to a sheet.
Specifically, a printer head having a liquid ejecting head in an inkjet printing system ejects a liquid drop during conveyance of the sheet made of various materials.
When an image is formed by such an ink jet printing system, a sheet sometimes expands and creates cockling due to moisture of the ink adhered to the sheet. The cockling causes waves in the sheet, and accordingly a positional relation between the printer head (i.e., a nozzle) and the surface of the sheet varies depending on a portion of the sheet. When the cockling reaches a worst case, the sheet can contact and stain the nozzle, and the head also stains the sheet, and therefore quality of the image deteriorates. Further, due to the cockling, a spotting position of the ink drop is displaced.
In order to maintain a sheet with an excellent flat surface, a seamless discharge belt is provided in an ink jet printing apparatus as discussed in Japanese Patent Application Laid Open No 2004-175494. Specifically, a charge belt electrostatically attracts a sheet, rotates the sheet, and conveys the sheet while preventing displacement of the sheet from the discharge belt.
Japanese Patent Application Publication No 2000-246981 discloses a copy apparatus that executes imaging on an imaging sheet while electrostatically attracting the imaging sheet by means of an electrostatic member at an imaging position to avoid occurrence of cockling and curling of the imaging sheet. The sheet conveying apparatus includes a switching device that switches from a mode in which an imaging sheet is attracted by the electrostatic attraction member to a mode in which an imaging sheet is not attracted by the electrostatic attraction member, vice versa, in accordance with a type of an imaging sheet.
However, an improved technique for avoiding cockling and curling of the imaging sheet is needed.